Biphenyl Cyclobutenone Photoelectrocyclizations

Abstract

In this work, we demonstrate that readily available conjugated bis-aryl cyclobutenones undergo photoelectrocyclization reactions to give the corresponding dihydrophenanthrene cyclobutanones when exposed to 350 nm light, TFA, and TMSCl. We have also found that cyclobutenone electrocyclizations and cycloreversions are in equilibrium.

Photocatalytic Electrocyclization for the Synthesis of Dihydrophenanthrenes

“…Rannier et al. also developed the photocyclization of conjugated cyclohexenone [5d] and cyclobutenone [5e] . However, the requirement of high energy UV light is a major drawback in these reactions.…”

“…6π‐electrocyclization of 2‐(1‐arylvinyl)benzaldehyde derivatives [6c] . In this manuscript, a method for synthesizing 9,10‐dihydrophenanthrenes through α‐addition [5d–e,7] to enones with 1,2,3,5‐tetrakis(carbazol‐9‐yl)‐4,6‐dicyanobenzene (4‐CzIPN) as photosensitizer is reported. The classical [2+2] photodimerization of enones was the major hurdle in realizing this transformation [8] .…”

Rearrangement of 2-(benzofuran-2-yl)-3-phenylpyridines via photoinduced 6π-electrocyclization

“…Irradiation of bis-arylcyclobutenones in CHCl 3 along with trifluoroacetic acid and TMSCl with a 350 nm UV lamp gave cis-2a,10b-dihydrocyclobuta[l]phenanthren-1(2H)-ones (Scheme 1d). 10 Last but not least, cis-dihydrobenzofurans were obtained by the irradiation of 2-aryloxyketones and an iridium(III) photosensitizer with visible light via the sequential 6π-electrocyclization, suprafacial [1,4-H] shift and epimerization (Scheme 1e). 11 Our group has been focusing on the synthesis of fused polycyclic and cis/trans-bridged cyclic aromatic compounds via photoinduced dehydrogenation and 6π-electrocyclization rearrangement.…”